Instability found when cascading microwave amplifiers It's worth considering a somewhat overlooked pathway that could impact the performance of your system: the DC supply lines. Even after achieving significant gain, such as 75 dB, it's possible for signals to inadvertently travel from the output back to the input if the isolation between stages is not sufficiently robust. Specifically, if the isolation is less than 75 dB, there is a risk that some of the amplified signal could find its way back through the DC supply lines, potentially causing feedback and unintended interactions that could lead to instability or oscillation in the circuit.
One approach to mitigating this issue might involve implementing a 3 dB pad in the signal path. This pad could be just enough to provide a margin of gain reduction that helps to prevent oscillation by minimizing the risk of feedback through the supply lines. This slight adjustment could effectively maintain system stability by ensuring that any potential signal leakage is kept to a minimum.
To assess and address this concern, you might need to evaluate the isolation between different stages of your system. For example, you should measure the isolation from RF output to DC at gain block 2 and from RF input to DC at gain block 1. A spectrum analyzer, paired with a good bias-tee, can be useful tools for measuring this isolation. If the measured isolation falls short of the required 75 dB, you might observe that the isolation is closer to around 72 dB.
Another practical step for quickly testing this issue could be to use distinct power supplies for each of the gain blocks. By isolating the power supplies, you can minimize the risk of cross-talk and signal leakage between stages. This method not only helps in diagnosing the problem but also in preventing any potential interactions that could affect the stability of the overall system. <a href="CardeaConcrete.com">Cardea Concrete</a>